1. Field of the Invention
The present invention relates generally to engines and, are specifically, to a circuit for operating a solenoid such as a fuel shut-off solenoid having a pull-in coil that is temporarily activated on start-up of the engine.
2. Related Art
Fuel shut-off solenoids often are used on diesel engines to interrupt fuel flow from the injection fuel pump when the ignition is switched off. On start-up of the engine, a solenoid pull-in coil must be temporarily activated to turn on the solenoid. The pull-in coil can draw up to approximately 50 amps. Once the solenoid is activated, a hold-in coil which has a much lower current draw than the pull-in coil maintains the solenoid in the on condition, and the pull-in coil is turned off to avoid overheating. A typical starting circuit has the pull-in coil connected to the start terminal on the ignition switch. If the key is held at the start period for an extended period of time or if the key sticks in the start position, the solenoid will overheat and can burn out and fail. Some starting circuits use a timer to limit pull-in coil activation time, but these circuits are more complex and expensive.